reportAbstractUsage check ignores __new__ return type

[camillol]

Background

Some classes define __new__ so that calling the class always instantiates some specific subclass; for example, instantiating pathlib.Path always produces a PosixPath or a WindowsPath.

Here is an example.

Note that you can type __new__ as def __new__(cls) -> Foo | Bar, and pyright correctly understands that if you write b = Base(), b's type is Foo | Bar.

Describe the bug

However, if your base class is abstract, pyright reports a "Cannot instantiate abstract class" error, even if the class(es) it actually instantiates are concrete. Example

Expected result
I think the reportAbstractUsage check should base its decision on __new__'s return type. If it returns a concrete class, or union of concrete classes, it should not flag it as an attempt to instantiate an abstract class.